The invention provides a shape memory alloy step drive mechanism for providing step motion to a system.
Many step drive mechanisms are known in the art. Almost all of them uses electromagnetic components. In certain precise applications such as in space applications it is desirable to have non-magnetic components in such step drive mechanism. The invention provides a step drive mechanism which does not use any magnetic component. The step drive mechanism according to the invention uses a shape memory alloy element. Shape memory alloy is an alloy which is plastically deformed at a suitable temperature recovers fully or partially its original shape on subsequent heating, by solid state phase changes in the alloy. The shape memory alloy element is heated by passing electric current using pulses in order to actuate the step motion.
The invention provides a step drive mechanism comprising at least one shape memory alloy element with a fixed end, the other end of the shape memory alloy element being connected to one end of a lever, lever being provided with a pawl which is located to move on the teeth of a ratchet wheel mounted on a main shaft along with the lever, a stopper pin which also guides the pawl on the ratchet wheel, a bias spring provided on a mandril on the main shaft for returning the lever to its original position, a detent wheel with at least one detent lever mounted on the main shaft to provide the detent torque required to hold the main shaft in position when the lever returns to its original position and a pair of support brackets for supporting and holding the said components together in an assembly.
The desirable step movement of the main shaft is achieved by pulse width modulated heating of the shape memory alloy element which ensures uniform heating and long life of the shape memory alloy element. In a prefered embodiment two shape memory alloy elements are used one for the step movement in clock wise direction and the other for step movement in the anti-clock wise direction.